The need to reduce fossil fuel consumption and emissions in automobiles and other vehicles predominately powered by internal combustion engines (ICEs) is well known. Vehicles powered by electric motors attempt to address these needs. Another alternative solution is to combine a smaller ICE with electric motors, such as an electric traction motor into one vehicle. Such vehicles combine the advantages of an ICE vehicle and an electric vehicle and are typically called Hybrid Electric Vehicles (HEVs).
The HEV is described in a variety of configurations. Many HEV patents disclose systems where an operator is required to select between electric and internal combustion operation. In other configurations, the electric motor drives one set of wheels and the ICE drives a different set.
Other, more useful, configurations have developed. For example, a series hybrid electric vehicle (SHEV) configuration is a vehicle with an engine (most typically an ICE) connected to an electric motor called a generator. The generator, in turn, provides electricity to a battery and another motor, called a traction motor. In the SHEV, the traction motor is the sole source of wheel torque. There is no mechanical connection between the engine and the drive wheels. A parallel hybrid electrical vehicle (PHEV) configuration has an engine (most typically an ICE) and an electric motor that work together in varying degrees to provide the necessary wheel torque to drive the vehicle. Additionally, in the PHEV configuration, the motor can be used as a generator to charge the battery from the power produced by the ICE.
A parallel/series hybrid electric vehicle (PSHEV) has characteristics of both PHEV and SHEV configurations and is sometimes referred to as a “split” parallel/series configuration.
In one of several types of PSHEV configurations, the ICE is mechanically coupled to two electric motors in a planetary gear-set transaxle. A first electric motor, the generator, is connected to a sun gear. The ICE is connected to a carrier gear. A second electric motor, a traction motor, is connected to a ring (output) gear via additional gearing in a transaxle. Engine torque can power the generator to charge the battery. The generator can also contribute to the necessary wheel (output shaft) torque if the system has a one-way clutch. The traction motor is used to contribute wheel torque and to recover braking energy to charge the battery. In this configuration, the generator can selectively provide a reaction torque that may be used to control engine speed. In fact, the generator motor and the planetary gear-set can provide a continuous variable transmission (CVT) effect between the engine and the wheels. Further, the HEV presents an opportunity to better control engine idle speed over conventional vehicles by using the generator to control engine speed.
In traditional, non-HEV's, a common method to prevent unwanted driveline oscillations is to use an alternator generator as a counter-torque to eliminate driveline oscillations. For example, European Patent Publication EP 1077150A2 issued to Hrovat et. al. (“Hrovat Publication”) disclose various methods of utilizing a vehicle's starter/alternator to generate torque to power electrical devices. However, the Hrovat Publication does not apply to HEV's because the HEV does not require an alternator. An HEV already has a ready source of electrical power within its battery and can generate additional power with an onboard generator. Additionally the Hrovat Publication does not disclose use of a traction motor to control oscillations in the driveline, particularly during an ABS operation.
However, in the design of vehicles powered by electric motors it is desirable to have a high gear ratio that allows the motor to spin much faster than the wheels. A disadvantage of a high gear ratio is that it amplifies the value of motor inertia that is reflected to the wheels.
During antilock braking operations, the rapid cycling of the wheel speeds coupled with the high reflected motor inertia may cause deflections in the driveline. The resulting oscillation can cause unpleasant NVH and damage to driveline components or mounts.
One method of reducing unwanted oscillations is to either reduce mass of motor or to use a smaller gear ratio to decrease driveline deflections, however, this solution decreases the efficiency or effectiveness of the electric motor.
It is beneficial, economical, and efficient to have an apparatus, system and method that incorporates an HEV traction motor controller to output a counter-torque with the ability to damp out unwanted oscillations resulting from motor inertia in the driveline, particularly during an ABS operation.
It is common for vehicle traction motor controllers to include some sort of torque oscillation control feature in a motor torque control strategy. However, existing methods may operate to damp out driveline oscillations that occur during normal driving modes due to chassis vibrations or the like. The need to reduce oscillations that are induced by motor inertia of an electric motor in the driveline of a vehicle during an ABS operation remains unmet.